Peristaltic pumps are well known and comprise a rotatable drum having a plurality of rollers located around its periphery, and a flexible tube which is held against the drum periphery by a presser plate and through which liquid (for example) is pumped. The tube is held by two spaced fixed supports, and liquid is caused to move through the tube in response to a moving pinch zone caused by the rollers pressing on the tube as the drum rotates.
Pumps of the foregoing kind suffer problems which tend to make them unsuitable for use in certain circumstances. One such problem is a tendency for the tube to become distorted and to take on a permanent set which makes it unsuitable for further work. In operation, the tube is pulled over the drum and is attached to the fixed supports so as to have a correct amount of longitudinal tension. If the tube is left in the operating position for extended periods of time with the pump stationary, the aforementioned distortion may occur. Consequently, it is good practice to release the presser plate and the tube tension at the end of each period of use, but that is often overlooked either by accident or by design, particularly as the re-establishment of the pump to an operative condition is a tedious process.
Another problem with peristaltic pumps is that the output flow is a pulsating flow, and that tends to make such pumps unsuitable for use in some circumstances. For example, the pulsating flow makes such pumps unsuitable for use in delivering a sample to be analysed to the nebulizer of a spectroscopic instrument. That difficulty can be met by operating the pump at a very high speed but such operation is not always possible or convenient.
Another problem in peristaltic pumps that are to be used for accurately metering materials and which is a significant component in their cost, is that dimensional tolerances in the manufacture of individual components, such as the drum and the rollers, and positional tolerances on assembling the different parts are necessarily quite small to ensure the requisite accuracy in operation of the pump. Also the roller bearings in known pumps often corrode and produce unreliable operation.